this sounds like an allusion to the "leaked" (may or may not have been intentional) Goblin and Worgen masks that were found in PTR files in 2008, before the official announcement of Cataclysm, which lead to the jokeful addition of Ogre and Murloc masks in the next build.

The agility, intellect and strength buffs increase these respective stats by 35 at level 85. The stamina masks appear to give 61 stamina at level 85.These costs 5 Tricky Treats each and come in stacks of five.

For the Alliance, there is a level 1 NPC standing outside of the gates of Stormwind called Spanky <Mask Vendor> which sells these.The Horde vendor Farina can be found at the Ruins of Lordaeron in Undercity.You can also buy all the playable races-masks from these NPC's for 2 Tricky Treats each, which you need in order to complete A Mask for All Occassions.

Comment by Necropenguin

The buff this mask gives will stack with other Agility buffs. I didn't see anyone else saying whether they would or not, so I just tested them all.